Power has been making the rounds with McCain and other members of the Senate Foreign Relations Committee ahead of the panel's hearing on Wednesday. She would replace Susan Rice, who took over as Obama's national security adviser on July 1.

Opposition to her nomination has been led by Frank Gaffney, a former assistant defense secretary in the Reagan administration who heads the conservative Center for Security Policy. Gaffney and other Power critics, including former Rep. Allen West (R-Fla.), accuse her of being too critical of the United States and Israel but have failed to convince lawmakers.

Several of McCain's Republican colleagues on the committee agreed with his assessment.

Sen. James Risch (R-Idaho) called her a “very engaging person” after sitting down with her late last month.

“She has good qualifications, there's absolutely no question about that,” he said. “We had a really good discussion about reform at the UN – if you don't consider that an oxymoron – and she supports a lot of things that should happen” with regards to paring down the organization's size, reach and salaries.

Power would bring considerable expertise to the position. A Pulitzer Prize-winning author of books on genocide prevention and slain UN diplomat Sérgio Vieira de Mello, she worked on UN reform within the White House during Obama's first term.

As a result, her nomination is drawing international attention from countries that share U.S. interests in reforming the UN.

“I'm following her appointment because it's the first time that the U.S. will have a UN specialist as Ambassador,” a Mexican diplomat who tracks U.S. affairs told The Hill. “She knows the UN very well and that opens a window of opportunity for U.S. foreign policy. Mexico has always committed political and financial resources to make the UN functional and Power could be an important partner.”

Her appointment isn't expected to draw much objection from Democrats, despite her support for the controversial U.S. military intervention in Libya two years ago.